Processes for the production of ethyl acrylate by interacting acrylic acid with ethylene in the presence of sulfuric acid are well known; see for example U.S. Pat. No. 3,703,539 issued Nov. 21, 1972 to DiLiddo; U.S. Pat. No. 3,539,621 issued Nov. 10, 1970 to Cipollone et al; and U.S. Pat. No. 3,894,076, issued July 8, 1975 to Van Duyne et al. As described in these and other references, the reaction is believed to involve the formation of intermediate sulfates from the reaction of ethylene with sulfuric acid. These sulfates further react with acrylic acid to form ethyl acrylate. To provide a product in good overall yields with high carbon efficiencies, unreacted ethylene, acrylic acid and the sulfuric acid residue must be recycled to the reactor. Copending application U.S. Ser. No. 182,553 filed Aug. 29, 1980 and assigned to Celanese Corporation describes processing improvements of passing specific product residues to a wiped-film evaporator and the remainder, if any, back to the separation step of the crude ethyl acrylate and a sulfuric acid residue in the ethyl acrylate production from ethylene, and acrylic acid in the presence of sulfuric acid.
In the above processes, the acrylic acid used normally contains inhibitors which prevent undesired polymerization prior to use. The inhibitors commonly used are phenothiazine, methylene blue, phenolic type inhibitors such as hydroquinone, p-methoxyphenols and the like. It is not generally known to use a metal additive in combination with organic inhibitors in acrylic acid. In Chemical Abstracts Vol. 74, 1971, 112642V, a Japanese patent (70-35,285) filed June 1, 1967, assigned to Nippon Kayaku, Co. Ltd., describes the mixture of chromium acetate with hydroquinone as a satisfactory inhibitor for acrylic acid and methacrylic acid. In Japanese Patent Publication No. 51-98211, filed Feb. 15, 1975 assigned to Sumitomo Chemical Co. Ltd., the combination of a manganese salt and phenolic type inhibitors provided satisfactory stabilization of acrylic acid. In copending application Ser. No. 06/510,870 entitled "Stabilized Ethylenically Unsaturated Organic Compositions" filed July 5, 1983 and assigned to the same assignee as the present application, describes the use of cerium in combination with other inhibitors as an inhibitor for polymerizable ethylenically unsaturated organic compounds. In this invention, however, improvements are achieved over the above described and known ethyl acrylate production techniques using manganese and cerium ion additives soluble in the reaction mixture.